The present invention relates generally to semiconductor fabrication and more particularly, to a processing chamber that is configured to reduce re-circulation cells and dead zones in the process gas flow pathway and to enable uniform heating of a semiconductor substrate.
In the fabrication of semiconductor devices, a variety of processing operations are performed in processing chambers such as deposition chambers, etch chambers, cleaning chambers, etc. The design of the processing chambers used for these operations is defined by a flat top such that a cross sectional view of the processing chamber will be square or rectangular. The corner regions of the reaction chambers harbor re-circulation cells and dead zones where stagnant species can linger due to the fluid dynamics in the reaction chambers. Reactions between the stagnant species in the re-circulation cells and dead zones ultimately lead to the formation of particles during the processing operation. In turn, these particles can land on the surface of the substrate being processed which may ultimately lead to reduced yields and lower throughput.
FIG. 1 is a simplified schematic diagram of the airflow in a processing chamber having re-circulation cells and dead zones. Processing chamber 100 includes gas inlet 102, heating lamps 106 and substrate support 104. During processing operations, process gases flow through inlet 102 toward substrate 116, resting on substrate support 104, as indicated by arrows 114. The fluid dynamics inside chamber 100 lead to re-circulation zones 110 (also referred to as eddy currents) and dead zones 112. Re-circulation cells 110 have a long residence time leading to gas phase reactions and homogenous nucleation which results in particle formation. These particles tend to reside inside chamber 100 in areas that lack a purging fluid flow such as dead zones 112 and re-circulation zones 110. Eventually, the particles fall onto the surface of semiconductor substrate 116, thereby contaminating the semiconductor substrate.
Another shortcoming of the flat top reaction chambers is the uneven temperature distribution from heating lamps 106, which are disposed on the top of the chamber as shown in FIG. 1. Since the top center region of chamber 100 is used to introduce process gases over the surface of substrate 116, heating lamps 106 direct the radiation through windows 108 toward the edge of the substrate. As such, the temperature profile across semiconductor substrate 116 is uneven. In particular, the center region of semiconductor substrate 116 is cooler than the outer edge of the substrate. The temperature near the edge of the substrate can be greater than 10 degrees higher than the temperature at the center of the substrate. This temperature difference between the center region and an edge of the substrate is amplified as the semiconductor industry transitions from 200 millimeter wafers to 300 millimeter wafers. The non-uniform temperature profile impacts the process parameters, i.e., removal rate, etch rate deposition rate, etc. Consequently, a non-uniform temperature profile leads to a non-uniform processing rate.
One attempt to compensate for the temperature effect on a processing rate is to direct more of the process gas flow toward the center region of the substrate. Thus, the reaction rates at the center region are driven higher through the higher concentration of process gas, thereby attempting to equalize the increased reaction rates near the edge of the substrate due the higher temperature. However, the process gases are expensive and require treatment prior to release into the environment. Accordingly, it would be desirable to limit the amount of process gases consumed in the semiconductor fabrication operations.
In view of the foregoing, there is a need for reducing the occurrence of re-circulation cells and the dead zones within reaction chambers during semiconductor processing. In addition, there is a need to provide a substantially evenly distributed temperature profile across the surface of the semiconductor substrate during processing operations.
Broadly speaking, the present invention fills this need by providing a sloped top having a sloped surface that allows continuous purging of dead zones. Additionally, the orientation of heating lamps disposed over the sloped top provides for a substantially uniform temperature profile across a semiconductor substrate being heated.
In accordance with one aspect of the present invention, a chamber top is provided. The chamber top includes a top surface and a bottom surface having an inner and an outer edge. The bottom surface is sloped downward from the inner edge to the outer edge. A central opening extends through the chamber top. In one embodiment, the downward slope is between about 10 degrees and about 20 degrees.
In accordance with another aspect of the invention, a chamber for processing a semiconductor substrate is provided. The chamber includes a base having an edge. A sidewall extends from the edge of the base. A top is disposed over the sidewall. The top includes a top surface, a bottom surface having an inner edge and an outer edge, and a central opening extending therethrough. The bottom surface is sloped downward from the inner edge to the outer edge.
In accordance with yet another aspect of the invention, a method for processing a wafer in a process chamber is provided. The method includes the operation of flowing process gases along a surface configured to reduce stagnant species formed by gas phase reactions between process gases. In one embodiment, the surface is a sloped surface.
In accordance with still yet another aspect of the invention, a method for uniformly heating a substrate in a processing chamber is provided. The method initiates with affixing at least two heating lamps on a chamber top. The at least two heating lamps are affixed such that each of the at least two heating lamps are disposed over a window configured to allow heat energy into a processing chamber. Then, the at least two heating lamps are oriented such that an axis of each of the at least two heating lamps is directed toward a center region of a substrate in the processing chamber.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.